Some time ago, the old Sudoku Players Forum disappeared into a really nasty commercial site. Most of the messages have been recovered, and are posted at the new PlaySudoku Forum. However, you will still find broken links to the old site.

Those links look like this:
http://www.sudoku.com/boards/viewtopic.php?p=64249#64249

The new link is like this:
http://Forum.EnjoySuDoku.com/viewtopic.php?p=64249#64249

In other words, replace
www.sudoku.com/boards
or
www.sudoku.com/forums
with
Forum.EnjoySuDoku.com

If the link you are looking at is aliased, quote the message to see the actual URL